No repercussions just chuck your own bank statements in showing liquidity for the length of stay if possible do a hand written letter stating things like you take full responsibility for her, we have been in relationship for x time , travel both ways together, estimated travel dates BUT don’t lie
Just make certain you are still on the electoral register at that address. Remember that once you live in Thailand for more than 180 days a year you will be a tax resident. Thailand has signed up to CRS and therefore shares all your bank accounts and tax returns with the UK and vice versa.
She has to apply via the UK government website and make an appointment at VFS Global in Bangkok to submit documents and get her biometrics taken. The visa costs around £110 and there are charges for biometrics, translating any documents and also for any copies needed.