From my e-mail correspondence on italki:
My attempt at translation: "Even though I thought that 「友達申請をしてくださって、ありがとうございます」 might be a bit hard, because I think/thought that from there on...
A)...there is the chance you use it... B)...you have the opportunity to use it...
...I wrote it that way. I'm glad you picked it up."
First: What's a bit irritating for me is that in this full sentence, there is present tense all of a sudden in ...と思うので.... I know from my past questions that japanese isn't too strict in the use of tenses, but I would like to know why there is this sudden switch and what it expresses.
Second: I wonder wether I should use ある in the meaning of "existing" for inanimate things, or in the meaning of "owning". Or are both meanings basically the same in japanese? In my textbook, I once learned for ある that it can express ownership (at least I think I did...^^) over the associated object. But maybe this "extrasemantics" was just a means to make it easier for the learner of japanese to understand the different functions ある appears in.
Third: In 覚えてくれてうれしいです I think she expresses that she's happy that I picked up the grammar she had shown me. However, I just wanted to ask for confirmation wether my understanding, which I tried to convey with my translation, is correct or not, since the combination of "memorizing" and "giving a favor" seems a bit strange to me. So I don't know wether I should trust my understanding or not ^^