Clarify your question, please. The mom, family, cell phone, Nevada part is unclear.
As for StraightTalk...
Generally, when you add airtime to a StraightTalk phone via a service plan card (their term for it), you simply call the number on the back of the card and provide either your existing StraightTalk cell phone number or the serial number to a previously unactivated phone, and then give them the PIN number on the service plan card.
If they are requesting a receipt, either your phone or the service plan card likely wasn't activated at the time of purchase and the phone/card is showing that it's not a valid, activated piece of merchandise. (When you buy a StraightTalk phone or a service card, at the time of purchase the serial number gets entered into the cash register system and the item gets activated via that system.)
If that's the case and the phone/card is not returning an "active" status in their system, then it would appear to them that it is stolen, and that's likely why they are requesting a receipt to prove purchase of the phone/card.