Water left after boiling eggs is not a measured fertilizer. Let it cool and check for salt or additives rather than promising stronger flowers from its mineral content.
Boiled egg water is still unmeasured
The composition of water left after boiling eggs varies. It should not be described as a complete mineral feed or a reliable way to extend a flowering season. A visible plant response cannot be promised from one leftover liquid.
Check before any reuse
Never put hot water on a plant's roots. Consider salt and other additives, residues and how the water has been stored. Water that is unsuitable for the intended plant should not be reused simply to avoid waste.
Keep feeding purposeful
Use an appropriate water source and feed according to the actual plant's needs. Follow a suitable fertilizer label when nutrients are required. A struggling plant also needs a check of light, root health and drainage; extra kitchen water cannot resolve all of those problems.
Related reading: Rice Water for Plants: Nutrients and Practical Limits.