How to let down a sweet girl?

Hi Reddit, I'm needing advice about how I can let a nice girl know that I'm not interested in dating her anymore.

Backstory: me 25M, her 22F. We've gone on about 5 dates, have slept over at each other's places once each and up to now has gone pretty well. I was enjoying her company but eventually I have started to see a lot of parallels to my ex-gf which has made me less interested. To add to that, she's a very shy girl, and although I can assume that there would be an eventual payout (her being less shy and opening up to me) I'm just not really interested in putting the time and effort into making this happen, when it's becoming clearer to me that we're just not very compatible.

I want to know if there's a good way in letting her down gently, or what exactly I can say to her to let her know in a nice way that I enjoyed her company but I'm not really interested in seeing her anymore. (Without sounding like it's a line... even that last sentence kinda sounds like a line to me.)

The last correspondence between us was her asking me for a coffee, and me politely declining, inquiring about her day and then not answering after she answered with a one line answer.. I guess I could basically just not really answer and I would assume that this would be the end, but I kinda feel like I'm a jerk if I don't at least let her know that I'm not interested anymore.

Also, would it be me txting her this out of the blue, or should I wait until she txts me again? I think that after this short of time It's not really necessary to to this over the phone or in person.. right?

Anyways thanks a lot for the time to read this and any insight you have on this.