The talented 15-year-old, who is the daughter of Colchester United boss Danny Cowley, has signed for the Gunners after they agreed training compensation with Chelsea FC.
Isabella, a former Essex County player, was also offered the chance to sign a further two-year contract at Chelsea along with offers from Brighton and Hove Albion and Manchester City.
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However, the promising centre-half, who this season captained England U16 in addition to playing for the year group above in their U17 European Championship campaign, has now chosen Arsenal to continue her football journey.
Isabella said: "It was a really hard decision to be honest, because they are all really good clubs.
"It was a really tough call, whether to leave Chelsea or whether to stay. I had two brilliant years at the club and improved so much.
"I'd played against Arsenal U21s in the final weeks of last season and I really liked how they played; it was a really tough match.
"After I was given permission to speak with Arsenal, it was clear they really knew my game and how I would fit in with their style of play.
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"I also thought that it fitted quite well as we were planning on moving back to Essex because of my Dad’s work.
"The coaches seemed really nice and lots of the girls from my England team were going to Arsenal, so I thought it was the right decision.
"I'm just going to keep training really hard, playing well and hopefully keep getting selected for England and go from there.
"The women's game is growing all the time and I'm just lucky to be part of it.
"In previous years, it was a lot harder to be a girl playing football but after England winning the Euros a couple of years ago, it's really taken off and there are so many better opportunities.
"Arsenal women often play at the Emirates and get massive crowds there and I feel like there's more potential for first-team opportunities in the future.”
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It has been a busy time for Isabella, who has had to juggle her blossoming football commitments with her schoolwork.
She said: "I've just finished my GCSEs and it was quite a challenge trying to fit in both because of all of my football commitments but it was just a case of trying to find the right balance.
"I missed so much school due to training, games and camps but when I was there, I just got my head down and stayed focused and it was the same with my football.
"I tried to keep them both separate; if football wasn't going so well and maybe I'd had a bad training session, I wouldn't let it affect school or if I didn't do quite so well in an exam, I wouldn't take that into my football."
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Isabella flourished playing for Hampshire-based team Atalanta Sports, where she was coached by Danny.
She added: "I played for a team called Atalanta Sports where we played against the boys and played Saturday and Sunday every week, so it really helped me improve.
“Due to moving around the country for Dad's work, I’ve had six schools and played for so many different clubs. Each has contributed to me as a player and I’m grateful for my pathway.
"It's obviously so beneficial to have my Dad and my uncle Nicky around – they know so much about the game and have literally taught me everything I know.
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"My mum enjoyed a career as an international athlete as well, so she is able to support me away from the pitch teaching me how to live as a professional sports person.
"My Dad likes to give me tough love! There's no telling me I've done well, if I haven't - he just tells me how it is, every day.
"I like it this way and it has made me more resilient. Ultimately it gets the best out of me so I'm grateful for that, even if I don't always appreciate it at the time!"