Nearly 7m and sleep deteriorated 3 weeks ago...
This has coincided with the start of weaning? The two could be correlated. Either a food intolerance or a lack of calories.
Don't replace milk feeds with solids, have them in addition. Most calories are likely to come from milk at this early stage in weaning. Milk intake should be maintained at the level it was before weaning, or may even increase.
Offer a wide range of food groups, not just fruit and veg (which are low calorie). Lean meat is also low calorie but protein is essential. Lots of dairy and high fat, high calorie foods.
After these food issues have been checked, the main root cause of the problem is the fact baby does not go to sleep in the cot. If you want an independantly sleeping baby, they need to go to sleep independantly.
You at getting lots of years at bedtime anyway, so I would ise those years productively to teach your baby (a) how to relax in order to sleep and (b) how to go to sleep in the cot.
I would night wean and completely seperate feeding and sleeping. Feed upon waking up in the daytime. Then at bedtime feed before bathtime, before going upstairs, right at start of bedtime routine.
Then at sleep time, place baby in cot awake. Fully awake. Armed with a dummy place one of your hands firmly on baby's chest/back/side. Don't push down, but baby wants to feel the weight of your hand - so that in time she can close her eyes but still feel you are right there.
Spread your fingers wide, cover a large part of her torso with your hand, nice firm hold. If she is especially wiggly you can add in the other hand on her thighs/legs.
This is both reassuring for baby, but also physically teaches baby to be still and calm to go to sleep. It's not dissimilar to pinning baby down, just in a kind and gentle way. It's about teaching baby to lie still, not move around. So no getting up, no rocking on all-fours, no squirming around. Just stillness and reassurance.
There may be crying. But you are right there and you are armed with dummy. Keep reinserting dummy as needed.
Keep your body language caring and compassionate. I would lie on my bed next to the cot, so my body is physically next to baby's. Constant eye contact, watch baby at all times, with a caring 'It's ok, mummy is here' look. Ideally this wants to place you at the same eye level as baby - so lying on a bed next to the cot is great for this.
Bits of shushing and face stroking maybe if needed, but mostly I favour stillness and silence. No noise from you, minimal movements.
And just wait. Stay there right through until fully asleep. Wait through the crying. Reiterated the compasionate "I'm here for you, I care for you" body language with eye level eye contact all of the time. Firm hand/s, still, calm and dummy sucking in the cot - all the way from awake to asleep.
Then repeat every wake up, every nap time and every bedtime.