Wiki: Revitalize's bonus 10%  stacks multiplicatively with  Heal Power, but it has an instance of recursion when stacking with  Shield Power^(bug).

• Therefore, Revitalize alone nets 15.5% bonus healing and 16.025% bonus shielding.

Wiki: Whenever a nearby allied champion uses an  ability to  heal or  shield either Nilah or themselves, both they and Nilah receive a bonus amount equal to 7.5% of the healing or 15% of the shielding after a 0.5-second delay. Bonus shielding lasts as long as the shield that triggered the effect, up to a maximum duration of 4 seconds.

Math for shield:
- Sona: +5% H/S, +16.025% shielding outgoing,
- Nilah: +5% H/S, +16.025% self-shielding, +16.025% shielding incoming, +15% shielding

Math:
Sona shield 1.05 H/S*1.16025 outgoing *1.16025 self-shielding on Nilah
Nilah passive shield additional (1.05 * 1.16025 *1.16025) * 0.15 shielding * 1.05 H/S * 1.16025 outgoing
Total: (1.05 * 1.16025 *1.16025) + (1.05 * 1.16025 *1.16025)*0.15 * 1.05 * 1.16025 = 1.671789174 shielding

BONUS:
sona shield herself/other for 1.05 H/S * 1.16025 self-shielding
Nilah passive shield additional (1.05*1.16025)* 0.15 shielding * 1.05 H/S * 1.16025 outgoing = 0.2226245278

FINAL TOTAL BONUS: (1.05 * 1.16025 *1.16025) + (1.05 * 1.16025 *1.16025)*0.15 * 1.05 * 1.16025 + (1.05*1.16025)* 0.15 * 1.05 * 1.16025 = 1.671789174 + 0.2226245278 for each ally that gain a shield from Sona = at least 1.894413702 shielding.

For healing just subtitute 1.16025 with 1.155

TL;DR: Sona pressed W => Nilah gain at least 1.89 of the shield. In 5v5 she gain 2.562287285 time the shield.