If a wife forgives her husband for cheating on her is she weak or strong?

Smart

Neither.
Her forgiveness has nothing to do with strength or weakness.

Forgiveness is too complex in a circumstance like that. 
For instance, what is the cultural, religious and family background of each spouse?

There have been times, and there still are some places where a spouse's straying is accepted as long as the family sticks together and the children are cared for until they've grown up and got jobs. It's common in Italy. Tends to be more common where divorce is illegal.

In some religious families, the pastors, priests, rabbis, imams will pressure the wife to forgive so long as the husband genuinely repents and changes his behaviour.

Some people make an unbearable hullabaloo about straying. A woman I knew haranged the man for two years -- so relentlessly that he just left anyway. And the idiotic thing was that both he and the woman he'd had a one night stand with were drunk. It was unlikely that they ever would have tried to repeat their tryst.

But what if the man's been having the affair for a very long time and keeping it secret. He has proven that he is profoundly dishonest and cannot be trusted. She'd be wise to forget forgiveness, leave, and take the kids.
 
Or what happens if the man gets his mistress pregnant, or gives his wife herpes or aides? It would take a saint to forgive that.

There's never a simple answer to these things. Every couple has to work things out according to their values and the specifics of the situation.

IMO...Comme ci, comme ça, a French phrase that literally means like this, like that. In conversation, it means so-so, or neither good nor bad.

Could be What's good for the goose is good for the gander.

It could be either, or perhaps both.

I think she's strong, but forgiveness doesn't mean she has to stay in that situation.

I forgave my spouse for cheating even though we're not together anymore.
People are weak when it comes to love and sex from what I've seen and experienced.

However I never forgave her for lying about where she was going and for taking advantage of me and neglecting our child for so many years while she was cheating.
Those things she could have controlled in my opinion.