It will cost you more just to send it really almost with WU.

Easiest is to her Thai bank account using internet banking....all you need is her SWIFT code and address and account number.

Yes its what used to be known as a wire transfer and yes typically there are charges, but far less than the likes of Western Union who are bandits 

Dont put money in the post, thats just fking daft

If your in Thailand or have access to a Thai account via online just transfer...if in Thailand ATM to ATM or online tyoically costs Thb 25, if your doing an international transfer tor thb 2000thats when it will get expensive relatively speaking  

Yes on small amounts like a few thousand baht you may end up better off with someone like transferwise or bahtnet. They tend to build their profit into the exchange rates rather than charge a fee.

On the other hand if you are transferring large amounts say thousands of pounds / dollars you will like find that you end up better off doing a SWIFT transfer/ wire transfer. Ensure you send in GBP/ dollars and it is converted to THB at the onshore THB rate though.

As an example on a SWIFT transfer it may cost you say 10-20 pounds. On 10,000 pounds that's not much. 0.1% to 0.2%. However if you're only sending 50 pounds then that's still a 10 t 20 pound cost so 20% - 40%. i.e that fixed fee is a killer on small amounts but peanuts on larger amounts to get you a better rate

Western Union tends to be very poor value full stop

Dollar is strengthing against the THB could get to 36/36.4 before year end 

My dear Smokes you should be more specfic then in your orginal question, not all of us are interested in the Great British Riyal 

Well your being shafted to a degree then in current trading its 45.057, to be honest think this is as good as its going to get for whats left of this year and it will back off the 45