I can totally relate.. My advice is to clear your homespace (energetically), particularly where Layla sleeps. Stay connected to spirit yourself, meditate and clear your chakras etc.
Read and talk to her often about the spirit world. Angels, Fairies and Unicorns etc. I have also seen that children respond very well to crystals, so you could use them in her room and playspaces. (Careful with tumbled stones though in case they end up in the mouth)
I have also found that diet plays a big role in keeping the connection. Reducing toxins from the diet and any artificial ingredients. Dairy foods tend to block the third eye, and eating meat or too much of it, lowers our vibration which I believe makes it harder to be energetically at a level where spirit can communicate with us, or rather where we can hear, see or sense them clearly.
Using natural products, reducing toxins in the home and garden. Using natural toys and art & craft supplies...
At 15 mths good activities would be gardening and painting and playing music... The other thing I would try to do is surround her in colour and also start meditation and chakra clearing with her. You can do it before bed or while breastfeeding etc. You can visualise and send each colour to each of the chakras for cleansing and energising, or just visualise pure white/golden light entering her crown and cleansing her.
There is so much more you can do specifically, like asking particular Angels for guidance etc. I could babble on all day and night if you want, but I'll stop now in case this isn't really what you were after.

And also I'm sure a lot of it you're already doing being on a Natural Parenting Forum hehe...
It tickles me pink to hear of other mums/dads who have realised how important it is to nurture this part of their children's spirit.
Much love to you and Layla
Angel x