The full-back, who is also a biology teacher at Ross High in Tranent, believes the opportunity to play in SWPL 2 offers her a better work-life balance.
"I was quite surprised to be handed the captaincy as I've only just arrived at the club so it wasn't something I expected," the 26-year-old explained. "I think Suzy (Shepherd) wanted someone with experience so I do have that under my belt.
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"I seem to be making my way around the clubs in Edinburgh. It's kind of always been circumstantial why I've left due to my job so there's never been any bad blood between myself or the clubs.
"I loved my time at Hearts, but with SWPL 1 moving to a much more professional environment, it would have involved me doing almost two jobs at once. I wasn't going to be on a full-time professional contract at Hearts so I can't afford to give up my job as a teacher.
"I couldn't commit to the hours Hearts wanted so I just want to enjoy my football with Boroughmuir. It's still at a high level which is what I want.
"It's amazing to see how far the women's game has progressed. To look at some of the stuff happening now to what it was like when I first started out at Hibs aged 16, it's just so different.
"If I was 15, I would be so excited about what the future holds for women wanting to make a career in football. I think the professional side of it has maybe just passed me by, but I know that some of the girls at Hearts will go on to make a career."
Williamson added: "We have to aim to challenge for the league. We came so close last year to being promoted and missed out in the last game, so we'll see what happens as the season wears on."