* Edit. I wrote the first section thinking she'd had the crabs for awhile and you'd planned with her to have food and sand to last for several weeks. So see my edit. I'm combining my thoughts for two different scenerios.
I would not fight this battle. You and she have an agreement. I think it's important to stick with it. If you bail her out now she learns that she doesn't have to do what she's agreed to do.
My granddaughter, at age 9 or so,had hermit crabs and all she had to do was feed and water them every day. They lived for weeks without needing a change in soil. She still had food for them and they died. No one was monitoring them and so we don't know for sure what happened but I suspect she stopped watering and feeding every day. She did get bored with them. It's also possible that they just died. Yes, a hard lesson of two kinds. But not painful for the hermit crabs. They don't have nerves like more advanced creatures. They're a good way to start in teaching responsibility.
Edit: after reading the suggestions about ways to remove them without letting them die I agree. Also, after reading Angeles T's post, I think they died because they were placed next to a window that would get opened and closed.
Perhaps you could let the dirt go and if she has food left tell her that she's to work now to earn more food in the next few days. I definitely would not advance her the money. She's shown that she's not trustworthy to honor her agreements including those involving money. If she's out of food she can feel them people food. I think they like greens and veggies in really small bits.
When we rescue our kids our efforts at teaching responsibility are ineffective. * see below
* I just noticed she's only had them a week. They don't need their sand changed yet and how can she be out of food? The small bag we bought lasted for a couple of months. Hermit crabs are small and don't eat much. And how is she out of money, after all that you described her getting, in just a week. She had money when you bought the crabs? She has the $5 from her father. Did she have gift money when you bought the crabs.
Perhaps you didn't talk with her about planning ahead so that she would have money when it was needed? If my plan was to have her pay for supplies then I wouldn't have let her purchase the crabs before she had sufficient supplies to last for at least a month.
I suggest that you rethink your plan for her and then discuss it with her. Since she's just had them a week, I think it's unfair to give a consequence now because you didn't help her plan ahead. She's young, this is a new experience. She needs your ongoing teaching and help with planning ahead.
I'd, first revisit what hermit crabs need. Did you get a booklet or have you looked them up in the Internet? Then I'd talk with her about how to take care of them over time. If she kept up with the food and water this week, I'd praise her for doing so and then tell her, let's plan for the next week and the weeks after that. Help her "budget" for their supplies.
We bought supplies at the same time we bought the hermit crabs, knowing that their care was long term. Kids need lots of direction when starting to learn money management and caring for creatures.
It sounds to me that the more important problem here is helping her learn how to budget her money. You mentioned Don Ramsey's form. If you don't already use his suggestions for teaching. Monitor as she goes along. Apparently she's blown her money up until now. Perhaps as a condition of getting hermit crabs is to have a certain amount in savings for their care.
I wouldn't get rid of the crabs now. I'd start over tho. And I'd work with her to set up a savings plan, not only for the crabs but also for saving as a part of a plan for money.