Jam walks and dashes extremely fast, has really fast normals too, use this to your advantage and rush them down relentlessly. Use knock down to stash up card, and spend cards for damage or fast overhead.
Jam has super quick meter gain, so spend that meter. Mostly use meter for offense though, if you're scared of getting pressured, you can stack DP card in advance.
Generally being defensive should not be your style, do scary things to make your opponent on edge works way better than observing for Jam.
Tips and Tricks
DP without card is NOT a reversal.
5P is 3f, you can jab people out of some situations.
If your DP is blocked, you can j236k it and airdash to get out, no need to spend meter.
You can jump cancel 2D on block, oh yeah you know what that means.
A hit 6H means a full card, even when it's not a counter hit.
Your dust attack is safe on block but short, use with caution, but often, a full air combo from Jam is both painful and cool.
Jam has no fireball or fast long range normal, so she will rely on speed indefinitely, keep her out.
Keep an eye on her meter if possible, she seems always got some to spend.
She's not a strong footies character, a solid ground game will take you far.
Anti-air on reaction for her IAD is NOT a good idea, block that approach or burst out.