delaying completion for 12 months.

[trimtops]

my buyer came and knocked on my door 2 weeks ago to ask if she could buy my house
she viewed it in March, loved it but couldn't access her funds
i then took the house off the market, and out of the blue she came round and i said she could buy it.

However, she can't access her funds until 2020.
But will exchange contracts in a month, hand over 10% to my solicitor, and then move in and pay rent, and then complete the purchase, as i say late 2020.
Now I trust my solicitor to oversee the purchase, but I want to ask a silly question and am too embarrassed to ask him

My question is, if anyone can help...why does he get to keep the 10% deposit as he has told me?
Why is it not given to me after we exchange contracts.

Thank you everybody for your comments, which I wrote down and took to my solicitor this morning.
He is totally confident that this will work. He has done it before, for longer completions.
I am a landlord of 2 properties already, so am ok with how tenancy agreements work, however, she is not classed as a tenant, but a licencee. The agreement is basically the same, just a more law-abiding term.
Whatever happens, her lawyer has to prove, without doubt, that the money for completion is and will be available when required. Her lawyer basically can be sued by mine if she can't complete on time.
When we exchange contracts and she hands over the £45K, come what may, she loses it, - even after 6 weeks and says the house is not what she wants, then she loses it and leaves.
The only problem that could possibly arise is...that she doesn't complete when she should, and as someone upthread says, refuses to leave, trashes the house. Then I would have to go through the courts to get her out, as per a normal eviction of a tenant.
But I then have £45K in my pocket to fix everything.
So, I am going to see it through, THE RED BARROW re the estate agents fees, my lawyer has told me this, but apparently time has lapsed, so I might get away with it.!
Thanks again for your comments
Apparently, she loves my house so much, she has a picture of it on her screensaver, it ain't that great :) !!

As this is a very unusual situation I'd suggest asking for a higher than standard deposit. Can she access 20% rather than 10? Will she be paying rent? Where will you live?

The only problem that could possibly arise is...that she doesn't complete when she should, and as someone upthread says, refuses to leave, trashes the house. Then I would have to go through the courts to get her out, as per a normal eviction of a tenant.

That’s a pretty enormous problem/risk though and I think you’ll find that £45k is a drop in the ocean if you need to fix things and take her to court.

Personally I wouldn’t touch this with a barge pole
And don’t see why with that deposit she can’t just get a mortgage in the meantime, so it rings massive alarm bells for me that there’s more to this than meets the eye.

Put it back on the market!

Why would she be more likely to trash the house than any other tenant?
Given that she has £45k more to lose than any other tenant, in providing usual tenant deposit and the exchange deposit?

Well if you can swallow losses and aggro carry on