I need help to improve a credit score.

One of the people on my (small) team of churners needs to go get a car loan. But, I recently convinced her to apply for 3 cards (a gold Amex, a BW MBNA MC, and earlier an SPG Amex, in addition to 2 more traditional cards). She also holds a mortgage.

I can't find this info elsewhere for Canada.

• Is the interest rate for a future loan going to be higher because of this mini app-o-rama?
• Should she try to reduce her credit limit? Will it make a difference?
• Should she cancel older cards? Will it make a difference?

Any advice, or direction to a good resource, or PM's, gratefully accepted.