I think you know in your heart she is gambling. In all honesty what is getting “proof” going to achieve? Even with iron clad proof an active CG will spin it every which way.
I also don’t think that marriage counselling would help as she is still very much in denial and until the addiction is being managed you won’t be able to make any headway.
Though it’s my son that is the gambler I still know how you feel. Like you are losing your mind as they are SO convincing and manipulative and make you feel like you are the one with the problem. If you can get yourself to a Gam Anon group where you are amongst people facing the exact same issues you can at least get some perspective and support. You will be amazed at the relief it can provide.
Right now everything in your home is all about her… there comes a time when it’s time to look after the rest of you and stop letting her and her addiction dictate your lives.
Keep writing and learning.