I had the same concern with my current grow - for me, autos always went into pre-flower about week 3-4 and flower week 4-5 ... my lady didn't go into flower until week 7! I wouldn't be concerned about your lady at all... autos WILL go into flower - but in their own time, unless you've done something stressful to them and they can't recover and since all you've done is some LST, you have nothing to worry about. Different strains will grow at different rates, even with autoflowers... (and they're all I grow).
No worries - good luck!