Not sure what to say.. I guess you need to be supportive. But I can see the reason why you have concerns.
I have no idea what the process is with IVF.. But maybe suggest she do some conselling before going down the path to parenthood? Maybe it will help her see that becoming a parent is something special & that she should wait & see if she finds someone who will want to be her life partner to share such a special time with. KWIM?

Goodluck with it. Good on you for being a supportive Mum