Diaper Rash Cream - Does It Expire?

There is an expiration date on the tube. I think your assumption is most likely right. If she is a first time mom I would doubt she wants to risk it. If this is her 3rd child she would be happy to use it (ha ha).

I don't know.
Some things break down over time - ever come across a bottle/jar of cream or lotion or shampoo in the back of a cupboard that was a few years old?
It might have separated, gotten runny or oily - certainly toss it out.
But some things are pretty stable - they have LONG shelf life - and sometimes I think the expire dates in some cases really are an excuse to have people throw out something so more can be bought.
I've used a 10 yr old jar of Vicks Vapor rub and it was as if it were new.
Same thing with Bag Balm - that stuff lasts forever and I don't care what any expire date says.
A cream might be more prone to separation or consistency change - ditch it if it seems like that's happened.
An ointment is more likely to be pretty stable and if the consistency seems good, I'd use it till it was used up.
Expire dates have a purpose but a lot of the time it's a CYA move for the manufacturer.

B. nailed it. I've had creams separate somewhat, giving them a consistency that wasn't "right," if they were too old. An expired cream like that won't hurt the baby but might be less efficacious and might have that weird separated consistency (some of it creamy, some of it oily). I'd just give her a new one!

Look at the pinched end of the tube, opposite the cap. One side of it will have a lot number, and the other side will have "EXP and a date". If it's a little bit past its expiration date, it probably is okay to use, if a little less effective. Usually the expiration dates are fairly conservative - they are probably more important for something you ingest vs. a topical treatment.

Check on the very very bottom of the tube, where it's crimped and sealed. That's where some of my tubes of stuff have a tiny date stamped on them.