Unfortunately, there's not really much you can do in your situation without the receipt.
I'm not entirely sure why your mother is freaking out to the extent that she is; as an adult who routinely goes grocery shopping and keeps a very, very close eye on prices... beef is very expensive. Meat in general, but any kind of beef is inherently expensive. If she only gave you $25 for all of that, that's cutting it pretty close. It's possible you bought a brand, or type of beef that's more expensive than what she's used to (sometimes it's easy to grab something other than the store brand, for example, other times the store will have numerous packages with different prices per pound, etc.), you could've also bought more than she's used to buying. You could've gotten a more expensive brand of taco shell, etc. etc. It could've gone for anything in that list, you could have just purchased slightly more expensive things than she's used to getting. Or, you know, her mental math could just be off...
... as for her sending your father to the store to figure out what you bought, it's completely and totally pointless. As someone who has been a cashier in several different stores, many different times: the cashier, if they're still there, is not going to remember every single item you bought. They go through too many items, too many transactions, and too many customers a day to remember that. Second of all, grocery stores do not keep a record of transactions in the way that people think they do. Even if you used a point/rewards card, it doesn't keep track of transactions. I know there's nothing you can do to stop your father from going, but it's completely and totally pointless for him to go, and it's ridiculous that your mother even sent him in the first place.
Unfortunately without that receipt, there's nothing you can do except continue to assert that you were honest and purchased what you were supposed to purchase, and that you accidentally misplaced the receipt. If you want, maybe ask her what brands/amounts of stuff she usually buys to see if you accidentally bought a more expensive brand, or purchased a higher quantity than she normally purchases, thus resulting in the higher cost. I'm sorry she's behaving so suspiciously of you, that's quite unreasonable. Either way, best of luck with this situation.