I think you have probably hit it on the head in that she was in a herd where she was kept 'in her place' and now in a more relaxed environment she is
feeling her feet a bit.....plus of course the 'terrible two's'
I also noticed it with Sioned when we moved Yards. At our 'old' Yard she
was in with a herd and quite firmly kept in her place. At times she was
moved to a field on her own and I began to see the difference. In the
end I decided to move Yards and she was then totally on her own for a while.
Several things I noticed then, she certainly 'looked to me' more for guidance but also felt her feet a bit more and although she has never been a bolshy
horse in any way shape or form he did test the boundaries a bit more.
Within about 6 weeks I bought Bertie anyway, at first he was definately
'the boss' coming in not having been long Gelded, and he certainly ruled
the roost, but things have changed over the last Year (Blimey where did
that time go) and she now 'moves him on' and is definately 'top Horse'...
Thankfully although she moves him on, and WILL kick out at him occasionally,
she never actually makes contact and its all for 'show' more than anything
else, its very rare she makes a 'stand' with me, but does occasionally, just
to test the boundaries have not changed I think...
Think its probably something most of them go through, bit like Children, lol, and you just need to stay consistant and not change the goal posts