I think the guidelines have recently changed and it is now considered okay to wean from four months onward. I had a discussion with my paediatrician (I don't live in the UK) about this a few weeks back at our four months check up and she was telling me that the initial guidelines were four months, as part of an initiative to combat allergies it was shifted to 6 months but that in reality all children are different as to when they are ready but it is generally recommended that you wait till at least 17 weeks (calculated according to due date, and not necessarily actual date) if you LO shows signs of being ready early.
I was going to wait till six months with both my boys. However that didn't happen. I weaned my first at five months (four and a half months according to his due date), he was definitely ready for it and loved his food from day one. My younger son started weaning two weeks ago at just over four months (closer to five months according to his due date). He was showing all the signs of being ready - he could sit up on his own in his high chair (this is apparently an important one), was grabbing at our food, trying to pull my hand into his mouth if I had food in it, drooling more than normal when sitting at the table with us and making chewing motions when we were eating. The chewing on his hands I ignored as he's been doing that since he first discovered his hands, similarly the watching us was the same, he did that all the time so when we were eating wasn't anything unusual.
Tbh if your LO is still satisfied with her milk I would be inclined to hold off for another few weeks or till she is at least the recommended 17 weeks and start properly then.