If indicated air speed does not change can the amount of lift change?
Your friend is right.  Wind shear will greatly degrade or increase the lift depending on the change in direction and velocity of the shear.

If you are flying at 50 KIAS into a 50kt headwind, your ground speed will be zero knots.  If the wind shears to perpendicular to your flight path, your airspeed drops to zero knots and you fall out of the sky.  If it shears to 180deg in, says a microburst your airspeed is now -50kts or 50kts from the tail end almost certainly causing a departure from controlled flight.  In both cases at low altitudes the result is almost certainly fatal.

Conversely, if you were flying at 50KIAS and had a 50kt tailwind and the wind then sheared 180deg to a 50 kt headwind, you would abruptly jump to an airspeed of 100KIAS.  The airplane would rise very rapidly; you would feel the vertical acceleration in your seat.  This situation isn't as dangerous as shearing to a tailwind at low altitudes/speeds but it could be dangerous if one was cruising past Vno (yellow arc) where there is a risk of structural damage to the aircraft.

Your friend is right; microbursts are very dangerous.  The combination of wind shears as much as 90kts and severe downdrafts in the apex of the storm make it one of the most hazardous weather phenomena an aircraft can encounter.  They can even be catastrophic to large airliners at low speeds.  On August 2, 1985, a Lockheed L-1011 TriStar encountered a microburst while on final for KDFW and consequently crashed, killing 137 people.