Actually, the hay should be green with no yellow mixed in. The greener, the better, although it should be well dried. It should be timothy or another long strand grass hay (timothy, blue, meadow, brome), but young pigs and nursing sows may be supplemented with alfalfa.
You can get better quality hay for much less money online than in a pet store. If you're lucky enough to live where good hay is harvested, a bale is a bargain even if you have to give a lot of it away.
The only pellets this forum recommends for people in the U.S. are Oxbow and KMS Hayloft. Both are available from Amazon, Oxbow is at pet stores, and KMS Hayloft is online.
They should get alfalfa pellets (or another calcium source) until they're six months old, then switch them to a lower calcium pellet.
Your mom should be aware that guinea pigs are herd animals, so she needs at least one more. They do MUCH better with another of their own kind. I hope she's not buying a pig -- there are hundreds of pigs in need of good homes in shelters and rescues, and she won't be participating in the horrible breeding and distribution chain the pet stores use. If she does get another, she needs to turn them both over and compare their private parts before putting them together -- guinea pigs get missexed all. the. time.
Here's some recommended reading for new pig owners:
https://www.guineapigcages.com/forum/threads/113176-Information-for-new-guinea-pig-owners