Give her water and ask why she got mad

You did in fact have water, and you quickly took off your backpack to dig it out. Once you'd found out the bottle, you went to hand it to her, before pausing as you realized she didn't have any hands to take it with.

"Um... Should I... How do you...?"

The girl shrugged. "If you're comfortable holding it up to my mouth, that would be easiest. Otherwise, if you could break the seal and then set it next to me I can manage."

You opened the bottle and then crouched down to hold it to her lips. She drank greedily, and after a few moments, the bottle was empty in your hands. You closed it back up and then tossed it back in your backpack.

"Thanks." She said. "I really needed that."

"You're welcome." You looked her over again briefly. "So... If you don't mind me asking, why did you get mad at your boyfriend?"

Her expression darkened and she glared out at the woods past you. "The jerk kept treating me like I was made of glass. Just because I don't have arms I must not be able to talk to strangers! Just because I don't have legs, I must not be able to handle rough sex!" She started yelling her complaints, then suddenly blushed as she realized what she'd just told you. "... I'm sorry. I have no filter."