Yes it is old and a little bit lame. But, because of that, it is also very cute when friends use it. She was laughing because she liked it. It is okay to use sometimes :3

"it is raining like cats and dogs here." it's wrong (like) "it is raining cats and dogs here." it's right Might be that..

1) As people have said, you should leave out "like". 2) It's an older expression, and not so common now. People do still say it, though. It's definitely not "wrong" English. 3) I find some native speakers don't expect language learners to speak idiomatically, using slang expressions and so on; and they are often surprised when suddenly an "everyday" expression or phrase is used. The laughter could have partly been due to this. I know when I first started trying to use "yojijukugo" in Japanese to try and sound more learned and literary (!), people would often laugh. There weren't really laughing at me, they were just surprised.

I don't think it sounds lame! Actually, that's one of the fun things about speaking with a non-native speaker; they develop interesting vocabularies depending on what they've learned. Every one is unique!

I don't think there's anything wrong in what you said, apart from the idiom being so common it might sound clichéd. You could just ask your friend, "well, what would you say?" I do have another rain idiom to offer, but it might be a bit crass for your friend.