The example of "hot" was misleading by a previous poster as Americans pronounce that word almost sounding like "hat".
They will make something between Polish Ola and Ala, and Ala is a different Polish name. Ola is a diminutive of Aleksandra, Ala of Alicja (Alice) :)
It should be just o. Clear o. Not like the name of the letter "o" in the English alphabet, where it starts to be Polish "o", but then goes to something closer to English "w", Polish "ł" or Polish "u".
You don't have to be perfect, the same as Polish people aren't perfect in English pronounciation. Think, how many Poles can correctly pronounce "th", or "a" in, for example, "man" (so that you can distinguish it from "men")? Just remember that you have to pronounce "Ola" as "Ola" (with short, clear "o"). If you pronounce it like in "coast", then if you want to spell this pronounciation in Polish, it will be something like "Oula" or "Ołla". By the way... let's get rid of "a" in "coast". You have "cost" with... something looking like exactly this kind of "o" which you need.
See: dictionary.cambridge.org/dictionary/english/cost - and play the recordings of the pronounciation. The American version is wrong (I mean, if you want to use the same vowel for Ola; in American English for coast it's correct), it goes too much towards "a", but the British version sounds - for me - perfectly OK. Even though the phonetical symbol present there looks like "a" wirtten upside down, this what I here is exaclty what is needed in your's wife name.