We have toothbrushes and soap, but underwear and pajamas for a 3-day trip? No. That's not reasonable IMO, especially if BM hasn't seen her in 7 months. Would she even know their sizes/tastes? At 13 years old, they should know how to pack what they need for a short visit. Because that's what it is.
One summer I was thoroughly annoyed because BM allowed SD9 to pack 3 outfits, 2 pajamas and 4 underwear for a 4-week visit. The crazy thing was, she had 5-6 pairs of shoes. We had just purchased TONS of clothes including underwear, over spring break, which the girls take 100% of to BM home, so it's not like she didn't have them. BM always tells SDs to "tell Daddy to buy you _______ [whatever clothing they need]" so I think either BM didn't look at SD's suitcase or wanted her to ask DH for more clothes.
Once we traveled to visit SDs for a 2-day trip. We were staying in a B&B 30 minutes away from BM's home and in the kind of one-horse town where the one general store closes at 8pm. The one night the girls stayed with us, they forgot to pack pajamas and toothbrushes, so they washed their teeth with a washrag and toothpaste and slept in their clothes. They were fine... and I'm pretty sure they won't forget those items again.
I'm sorry to hear that this might end up in an emotional roller coaster place after the trip. Hope you are able to enjoy your weekend!