E, unfortunately WikiTree only has space for 1 mother and 1 father per profile, although it would be nice to be able to connect biological and adoptive parents, so we have to choose. It is your choice, by the way, although most members would urge you to make the biological connection, since the main purpose here is to trace genealogy.
You have probably already seen that you can select a status value for parents - it can be nonbiological, or one of several other selections used for a biological parent. If you choose to keep the adoptive parents connected, please be sure that they are indicated as nonbiological so that the person's ancestors are not traced through them.
If you want to connect the biological mother, you will be replacing the adoptive mother and will want to mark the status appropriately. To make this change, go to the edit page and, on the right side where the mother is shown there will be a link to "replace/remove mother". Click that and you'll be able to make the change you want.
Whichever way you choose to do it, you can explain it in the biography and include a link to the unconnected parent. There is also an adoption template that you can use. I did a quick look for the link to it, but could not find it in the help index. I'm sure someone who knows where it is without a major time consuming hunt to find it will answer and tell you about it.
