@FredFriendly
Idk, she seems fairly normal, albeit a bit more aggressive/assertive then the standard girls you see in a lot of manga.
She is a bit lewd, but nothing too outlandish for their kind of relationship. Different people act differently with certain people because they either a) know little about them and are unsure of the perceived relationship between them, let alone what would be considered acceptable or offensive behaviour outside of their normal interactions. Or b) know them well enough to understand their relationship and what would be considered acceptable or offensive, and where that line is. For this pair, it is option B. They are not strangers, and have a decent relationship where eachothers personality has been understood for the most part. They seem to know what would considered "taking it too far" for the other.
Also, she seems fairly interested in him romanticly. She at least is comfortable enough to sit on him and comment about being allowed to touch eachother anywhere.
Most people wont do that even if they like a person as a friend. Only with specific and/or rare cases does this happen, and even then, it is either because they have a long history between them, one is confirmed to be taken and is serious about it, meaning all this is is just teasing, both have a lot of excess self confidence and wont get embarrassed easily, are actually that sexually liberal, drunk/inebriated, or they are 2 girls who are very close, plutonic friends. This is not really any of these. So it must be that she is romanticly interested to an extent. One of the usual signs someone is interested in you is from how much physical contact you 2 share, and how often you share it. If there is a lot, and it happens often, there is a good chance that they are into you.