Tell Birth Mom???

I need some advice. About 2 and a half years ago my husband and I adopted our daughter. Her birth mom was raped at 13 and we know basically nothing about the guy (medical history, etc...) and what we know about her is relatively limited to what we were given from the hospital. Since about 6 months, I noticed delays inhitting milestones. Having 2 other children, I noticed this quickly and kept the doctor informed, but I tried not to worry since I know all kids develop differently. Well, at 1 year, he finally acknowledged what I have been telling him for 6 months...there was a delay. She wasn't even crawling yet! So, I got her into physical and occupational therapy. We were told she had "low muscle tone" and for a year and a half we have been in therapies and running tests, going to specialists etc.. to figure out why and what more we can do to help her. She is now in speech because, likely due to the low muscle tone, her talking is delayed and understandably she is frustrated with her decreased ability to communicate. I have been trying to teach her some sign language, but her fine motor problems make it impossible to do more complex signs. She can sign for "eat" or "food" for example to let us know she is hungry. I have let her birth mom know about her delays and therapies and keep her informed of her progress. She doesn't know all we have done to try to diagnosis this and I don't think she understands how behind she actually is. She also has trouble with bowel movements. She is on meds to go and has had tests and been to specialists for that too. Some think it may be due to the low muscle tone, but we still don't know for sure. Here is the reason for the thread. Recently, she has begun having grand mal seizures. They are horrible and very scary, especially since she turns blue. They began Dec. 11th and we immediately alerted her doctors and soon got her in to the hospital for and MRI, EEG, spinal tap and various blood and urine tests to try to figure out why she is having these. She also has "the drops" where she just flings herself backwards, petite mal seizures and is on a couple different meds to try to control them. She has had some regression and just recently has started seeming more like herself. We still do not know why or what is causing this. Her pediatrician says it can be called "epilepsy" but that may not be the actual cause of the problem. We have had to put her in a bike helmet to protect her from the drops and falls. All this is very new to us and there are still so many unknowns. We have not said a word to her birth mom for several reasons. At 1st, we were just trying to get them to stop and she spent 4 days in the hospital. We do not know why this is happening and would have a tough time answering her questions. Also, she is young (16) and we do not want to scare her or worry her especially since we have spent 2 weeks feeling scared and worried and there isn't really anything anyone can do. We are doing all we can and we don't want her sitting around worrying. However, we don't want her to be in the dark either and we would need to explain why she is in a helmet in her pictures. (I send pix all the time). So, I would appreciate some advice from birth moms, especially ones who were young and from a-parents. What and when should we tell her? How much detail? We usually talk by email and letter. I would prefer to tell her by letter than email...more personal. Should we explain it when we send the pix (about the helmet and epilepsy) or wait for her to ask about the helmet? How can we help her not to worry? Should we wait till we know more? When we know WHY this is happening? How can we assure her we are doing all we can? It is so scary for us and we just don't want her to feel what we are feeling. Is there any good way to tell a birth mother there is a problem? Have any of you had a child that later developed problems? We don't want her to think we feel any differently about our daughter...we have been dealing with her "special needs" for a long time, but she doesn't really know the extent of it all. I read a post a while back where a birth mom worried they wouldn't love her baby anymore. That broke my heart and I would NOT want her to EVER think that!!! We just love our daughter so much and we know her birth mom loves her too...and we love her birth mom and want to do what is best for her...we just don't know exactly what that is. You just never know if your child (adopted or bio) will develop problems, be born with problems, or have some sort of later accident or injury that will cause problems. We might have had a bio child with epilepsy...and we certaily do not love our daughter any less! Oh, I just hate this. I want to help my baby and I don't know how! I want to fix this for her and I can't!!! Thanks for your advice.