The visa is good for 6 months but oncr in country permission to stay can extend for up to 90 days beyond that.

Leave and re-enter on or before 26th for your third entry, depending on when exactly you do this, you will be able to stay until mid or late July. (Assuming you get 30 day extension.).

Then leave again and come back in either visa exempt or on a single entry visa.

Thais and other ASSEAN nationals get a visa exempt entry for 14 days. No visa needed unless stay will exceed 14 days.

There is no charge for the visa exempt entry, but many land borders will try to extract a bribe. Whether they do so and amount will vary with the border. If she stands firm can probably get in without paying it but the delay this will entail might not be worth it.

Correction - Cambodia will give most ASEAN nationals a 30 day visa free stamp. Thais only get 14 days, but Laotians, Vietnamese and Malaysians, amongst others, get 30 days. Even though few members would be interested in this, I know there are a small number who have non-Thai ASEAN citizen girlfriends and wives, so this is worth pointing out that they are able to stay a full month, whereas Thais get a shorter stay.

Thais and other ASSEAN nationals get a visa exempt entry for 14 days. No visa needed unless stay will exceed 14 days.

There is no charge for the visa exempt entry, but many land borders will try to extract a bribe. Whether they do so and amount will vary with the border. If she stands firm can probably get in without paying it but the delay this will entail might not be worth it.

Correction - Cambodia will give most ASEAN nationals a 30 day visa free stamp. Thais only get 14 days, but Laotians, Vietnamese and Malaysians, amongst others, get 30 days. Even though few members would be interested in this, I know there are a small number who have non-Thai ASEAN citizen girlfriends and wives, so this is worth pointing out that they are able to stay a full month, whereas Thais get a shorter stay.

Cambodia like most Asian nations operates a tit-for-tat policy on visa-free entry. Whatever a Khmer national gets in an ASEAN member country is what is provided in return. Khmer only get 14 days in Thailand and thus the favour is returned.