Us Visa For Thai Gf, Long-term Stay In Us

I am moving back to the US in July or August. I am going to bring my Thai gf to live with me. I would like to get some views on what I should do from people who have already done it. The following are my two options:

1. Get a 10 year visa and stay with me as a tourist and leave and come back after 6 month entry is up.

- PROBLEM - I plan on marrying her in the next year or so and with this option I am afraid we may have a problem with visas in the future. I am also scared if we do get married while on a tourist visa she will have to change her status in Thailand and will have to stay there for some time alone. I have heard you can't change a tourist visa to a marriage visa while still in the US ( I may be wrong, if it is possible this would be the option for us, hands down).

2. Get a K-1 visa and then change status after we get married.

- PROBLEM - I heard it takes a while to get this visa. It may not be done by mid-July to early-August. I have to be back in the US in early-August and don't want her to have to come separately. If I send the forms to the US within the next couple of weeks, do you think she could get the visa by mid-July/early-August? ( I think this is the best option except I don't want to do it if it can't be done on time)

I would really appreciate any of your thoughts on either or both of my options.

Thanks!!!