Thinking of Dany's invasion of Westeros and the state of the country as of right now, I started having fun with the numbers of the remaining forces of Westeros.
The North:
The Boltons, Umbers, Karstarks, Starks, wildling and minor houses forces have been almost completely depleted. The remaining noteworthy houses are the Cerwyns and the Manderlys.
I want to say there are 2,000 Cerwyn men, but I have absolutely no idea where that number comes from. Let's just go with that number for the whole North.
The Riverlands:
Right now, most of the Riverlands forces are Freys :V
Adding to that whatever the Blackfish managed to get, and assuming most of the forces Frey gave to Robb came back, this should put the Riverlands at again 2,000.
The Vale:
Highly speculative, but someone once said that the Vale's army matched Robb's. And since they were untouched by any war until BastardBowl (and they still were pretty much untouched after that), they probably have around 20,000 men.
The Westerlands:
It seems other people speculate the Lannisters to have between 30,000 and 60,000 men. Don't know if that number is before the wars or not. Let's take the average and give them 45,000.
The Reach:
I think it was Jaime that mentions the Tyrells have the second biggest army of Westeros. Not accounting for the size of the Dornish army, as of this line in this post, the second biggest army is the Vale and the biggest the Lannisters. Let's give them a point between those two, I'd say 35,000.
The Stormlands:
An important portion of the Stormlands army was lost to the Blackwater, and the siege of Winterfell. Doubt that there is much more from them. Gonna give them another 2,000.
Dorne:
God, do they love to be different. Anyway, the Dornish numbers are all over the place. Apparently, GRRM has said that Dorne is as strong as the North or the Vale. That would put them in the 20,000 range. I think that's a nice number.
Summary:
North: 2,000
Riverlands: 2,000
Vale: 20,000
Westerlands: 45,000
Reach: 35,000
Stormlands: 2,000
Dorne: 20,000
Total:
Westeros: 126,000
Dany's army was around 8-9,000 before she got kidnapped by the Dothraki considering all the loses from the Harpies and whatnot. The Khalasaar she got is said to be 100,00 though it is not clear how many of those are fighting men. Everyone is assuming 50% of that are fighting men, so let's go with that. That puts 60,000 men on her side, and 3 goddamn dragons above her.
If and only if, the entirety of Westeros is summoned to fight Daenerys, There is a chance she could be repelled if for example they focus on the dragons first.
But, Dorne is likely to side with her, because feminism and Lannister hate. And I don't think anyone but the Lannister-Tyrell forces would even bother.
That puts the resulting armies in
Westeros: 80,000
Dany: 80,000 + 3 Dragons
Of course, this is mostly speculation and I may be wrong about half of it. But it was fun to come up with all of that, and I already spent too much time to throw it away. If those numbers are somewhat correct, she has a clear shot to invading Westeros, but it won't be pretty, and it won't be easy.