Columbia OmniHeat jackets are a little boxy and true to size, but with that bulky thermal lining.
Based on your height (4’8″) and weight (140 lbs) a **Medium** is probably your best bet for a standard fit. A bit long through the torso but the sleeves should be okay. If you want a tighter fit or will be layering a lot underneath, go **Small** but know it will be snug in the chest.
The fit in the chest and shoulders is key since you said you are a 40D. OmniHeat jackets may feel a bit stiff when they are new. If possible, check the Columbia size chart for “Chest” and “Length” measurements in particular, as their cuts can differ model to model.
Happy hiking! 🏔️