For context, her (28f) and I (28f) have been best friends for 5 years. I just got out of rehab last week and it was the first time we'd been apart like that. She drove me there, picked me up, she was my biggest support. I called her regularly and kept in touch whenever I could.
The other day, she texted me asking if I wanted to hang out. I was apprehensive because things have felt off but I still agreed. 3 hours later, she starts putting on makeup and new clothes, telling me she had to leave in 15 minutes. This kinda threw me off guard because 1. she'd never done that with me and 2. she was just mentioning it.

To her credit, she did invite me along but honestly, I wasn't feeling it. At that point, her leaving me for others already felt like abandonment and I got stuck in that perpetual headspace. 

Further context: we started a more intimate friendship about 3 months ago and boundaries have been discussed and placed. I never expect sex when we hang out, we both just go with the flow and if it happens, it happens, if it doesn't, it doesn't. But I am aware that my own insecurities play a role in this. It just felt so off-putting and moderately rude to invite me over just to tell me to leave 15 minutes before actually leaving. 

I was unable to verbally express this with her because I got super anxious and uncomfortable. I ended up texting her after I left, requesting that she not ask to hang out with me if she had other plans. She got defensive, apologizing with "I'm sorry you felt that way." and "I don't understand why you're mad."
I wasn't mad, I was genuinely hurt, so those responses seemed like a huge red flag.

I understand that she has other friendships, half her friends are mine too actually. I don't want to come off as controlling or anything. It just felt like blatant disrespect to our friendship and I guess part of me feels genuinely betrayed considering I'd been in rehab for 21 days and she preferred to make time for people she's been hanging out with since I'd been gone.

Am I overreacting? Should I shrug the whole incident off? Or is this a situation where we both need to sit down and communicate clearly and calmly? How should I go about doing that?