[The birthday coincidence]

How about this:

Her friends are 2, 25, and 49

She is 50

You are 38

[Six integer equations, Eight digits]

When I tried to work this out, I hit a dead end pretty quickly. Makes me think this isn't solvable. Maybe I'm missing something obvious...

BC - XP = XC tells me that P=0

If P=0, CV - QP = VG means V=G and GP-ZY=JY means Y=5

and then

CY - GM = ZP means M=5

So...P=0, Y=5, M=5, V=G

VJ - MV = QG becomes GJ - 5G = QG...that means J = 2G, therefore G must equal 1, 2, 3, or 4

But if G<5, we can't do the subtraction problem GJ - 5G = QG unless Q is a negative integer.

[Three-letter Tic Tac Toe - Straight version]

My first random effort netted ten.

BEN

ARE

DAD

After some work I came up with 15. I couldn't use some of these in a sentence, but they sure work with Words With Friends. Only one that isn't good is LIO.

B A L

R I A

O R B

[piece of cake]

If the cake was just a regular rectangle...

Would cutting a circle out of the middle be considered a "one straight" cut? To keep the numbers simple, if the cake were 2 feet x 4.71 feet, she could cut a circle with a 2 foot diameter out of the middle. You would then have a circle piece with an area of 3.14 feet, and the two side pieces with the same area.