Well, according to a chart I found on Wikipedia, She'd probably be in the Subsonic levels (as per your request less than Mach 0.8 or less than 610 miles per hour). But if you insist on her reaching Transonic levels, that's Mach 0.8-1.2 A.K.A, 610-915 miles per hour. The speed of sound (Sonic or Mach 1) is roughly 761.2 miles per hour. Make of that what you will (Just don't forget the vapor cone. It forms just before breaching the sound barrier, so at Transonic speeds, she'll have one).

FYI, the rest of the chart says Supersonic is Mach 1.2-5.0 (915-3,840 mph), then Hypersonic at Mach 5-10 (3,840-7,680 mph), then High-Hypersonic at Mach 10-25 (7,680-16,250 mph), then Re-entry Speeds at greater than Mach 25 (greater than 16,250 mph).

I doubt she'll reach Re-entry Speeds any time soon.