I agree with what everyone else has said. My parents are kind of the same way. They don't yell or lecture me, but they make it clear that they don't like me having my two Bettas.
The people close to us don't have to understand why we put so much money into a fish or two, but they should accept that it's our choice and we have our reasons. If its not hurting them then they should zip it and let it be.
If you haven't already I would try to calmly explain to your friend why you put so much money into Earnest. If she still doesn't back off use the "well I don't understand why you but so much clothes but you don't see me bitching about it" card. If she can't respect your choice then don't talk to her for a few days. It will either piss her off and cause more drama (in which case you have to seriously consider whether or not being friends with her is the best thing) or she will see just how upset you are and how important this issue is to you.