It is understandable that you are nervous, but it is your daughter's decision, not yours, so do be careful what you say. (This goes double on issues about breastfeeding!)
As for your own worries, there are upsides and downsides for everything but, in the vast majority of cases, epidural is very safe, and the knowledge that it is available is enormously reassuring to moms-to-be who have been frightened by Hollywood depictions of childbirth or other horror stories which people just cannot zip their lip about..
There is no real reason to worry because, if your daugher is contra-indicated for one, she won't get one, no matter how loudly she screams for one (I was that soldier). I have delivered with and without and I think it is a great thing that there is a choice for women. Some people suffer greatly in giving birth, some don't- she may not have one on the day, but it sounds like it is important to her to feel that one will be available, so I would advise you not to undermine that- she has very likely weighed up the pros and cons herself with her care providers before making her decision.
Enjoy your grandbaby.