She says she just wants to be left alone for awhile, how long should I wait?

Alright, I met this girl online. We talked talked on the phone about 6 times over like 8 days. The calls would last 2-4 hours+ and went late into the night. On Tuesday she came to see me (It went really well, we both liked each alot) The next day she asked me if I wanted to get ice cream with her ( So, I went to see her and we had another really nice date).. but right before I was going to leave... we were chilling in her car, we were both on our phones doing our own thing for a second, and she saw that I had just responded to another girl text. I text messaged another girl "Hey babe (kissy emoji)" while I was with her in the car. The other girl that i had messaged means nothing to me, and it just a dumb meaningless message that i send sometimes. I know I had only known the girl I was out with for 10 days, but I really like her. I wrote her an apology letter, Over text I asked if a could read it to her later, but she said she accepts my apology but doesn't need to hear it. I told her my heart was hearting really badly, she said hers was too, but she's over it now. Then she said she just wants to be left alone for awhile. So, my question is how long should I wait before I attempt to rekindle this relationship? One week? Two weeks? Does she even want to hear from me again? and what should I say when I think she might be ready? I feel terrible about the whole thing, because right before she saw that text she was talking about other date ideas for us, and that she was going to come see me next time... Any advice would help so much!
She says she just wants to be left alone for awhile, how long should I wait?
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