Well - you are getting lots of advice... but you did ask!
One thing that I guess I was wondering is - what would "proof" do for you? The reason I ask, is my daughter used meth (yep - smoked it, shot it, snorted it) for five years while living in our home, and I never knew.
When I started to suspect, I tried a drug test, and first she balked LIKE CRAZY (whats wrong with you? how can you ask me to do such a thing? of course I don't use? Who said I was using meth? They hate me, of course they are trying to get me in trouble...) then, she gave me the urine sample - and it "disapppeared" overnight. So I bought another test, and this time I SLEPT with the urine sample.
And it came up negative. That is because the stimulants (like meth, or cocaine) are out of the system in 2 or 3 days - far faster than I realized.
WHen I finally, FINALLY caught her - she had every reason in the world why the test was wrong. SHe was taking "diet pills", she was taking "vitamins" she was taking something a friend gave her from the health food store... the test was just invalid. :O)
Hard to believe I would fall for such lame excuses, but I really WANTED to believe she was clean! So I did as long as I could - until I just could not ignore the behavior anymore.
There are folks on here who posted about taking PICTURES of a spouse passed out with drug paraphernalia on their chest, with residue on their face... and the spouse claimed that the sober one was CRAZY and trying to FRAME him!!!
Denial is huge...huge ... .huge!!! On both parts.
So even if you find drugs - then what? I guess I am trying to warn you that it isn't as easy as saying, "here's proof, so now quit!".
What I finally did was put boundaries around the behavior... because I had such trouble "catching" my kid while using - but the behavior was the thing I really hated anyway.
You say she is going through money like a hot knife through butter - then perhaps you can put a boundary around that. After all, perhaps she isn't addicted to drugs, but is addicted to gambling... online or otherwise.
By not providing her any more money - she has to deal with the consequences of her own actions - you don't.
THere are lots of great posts at the top of this forum - they are permanent posts referred to as "sticky" posts. I urge you to read as many as you can - they contain a TON of information.
Addiction - whether to drugs or food or gambling or sex or whatever - is an extremely complex addiction. THere is a lot to know, and there are no simple solutions (else we wouldn't have this board, I think).
Your father has noticed something that makes him suspicious - that alone tells me that you are dealing with "something"..... and the more information you have, the more prepared you will be.
I wish you the best.