Any subsequent active frames, if there are any, do 25 damage.
She extends her arms over these 3 frames for added distance, so the closer she is to her opponent, the more damage she'll do.
Some characters have awkward hitboxes which are smaller than there position boxes, meaning somethimes you can't get close enough to hit on frames 15 or 16. E.g. you cannot hit Voldo's front for 45 damage, only 35
Tips: she is really fast but struggles at range. Try to stay close. You'll need all the damage you can get so practice your punishing. FC3B and 2_8 5B are your primary launchers. 1B+K and 44B are your nest evasive tools. 1A+B and 3B+K can be used for tech crouch. 66A+B has a very fast auto-step but is high and very unsafe. If you like spacing, 66A and 44AA are good whiff punishers (or FC3B if you have time)
11 - AA, A[A]
13 - K, crouch grab
14 - close 2A and 6K, far 6B
15 - 4K 3B is your standard combo. Also BB and sometimes 66B+K
16 - as above
17 - 6B+K, grab
13 - 2A, crouch grab
14 - 6K, 6B
15 - 4K 3B, sometimes 66B+K
16 - as above, WR K, 2B
17 - 6B+K
18 - as above
19 - FC 3B
Your b&b combos are FC3B, 66B+K and 2_8 5B, 66B+K. Your best throw is 214B+G 412B, 1B. 2B+G leads to massive combos if you can get the JF down.
X doesn't depend too much on tech traps, but the most common opportunities are after 33B. Use 66K as standard, and if your opponent starts teching left or right, use crouch grabs.
Finally, tailor your use of SXS to your opponent. It is a great stance for breaking turtlers, but useless against spammers (which most online players are).