"I am in her yard."
Übersetzung:Ich bin in ihrem Garten.
*Can you say...
I don't know if it varies by region at all, but here's how we use the words in Australia. I suspect it's the same in the US and the UK, but I'll need people to confirm that for me.
A yard is typically just an enclosed area behind a house. A yard could consist of grass, concrete, tiles, dirt etc.
A garden is an area set aside for flowers, hedges or vegetables to grow. Most yards contain at least one garden.
For example, look at these images:
Each image is of a yard, but only the parts set aside to grow plants could be called gardens.
This is a yard without a garden:
This website talks about how to make a garden without a yard:
At least in the US, a yard can also be in front of a house. Usually distinguished by front yard and backyard.